Theatrical stage equipment includes devices that are required to be raised and lowered prior to and during a performance to provide a desired scene effect. These devices include various rigging sets, for example, curtains, borders, screens, scene displays, and lighting fixtures. The rigging sets, which are generally coextensive in length with a proscenium opening of the theatre have substantial weight.
A counterweight rigging commonly used in the theater industry to lift objects overhead on a stage or other location typically comprises a head block, a counterweight arbor, a floor block, loft blocks, a batten, lift lines, a rope handline, and a rope lock. The batten, which typically comprises a pipe or rod, is supported along its length by a plurality of flexible ropes or wires, each associated with a pulley. An item that is to be lifted is attached to the batten on stage, and an equal amount of counterweight in the form of metal plates is added to the counterweight arbor carriage. In this balanced condition, the counterweight arbor can be moved with a minimum of effort by pulling on the handline. Depending on the weight to be lifted, the total amount of counterweight on the arbor carriage can be adjusted by adding or removing an appropriate number of counterweight plates.
Movement of the counterweight arbor can be accomplished either by manually pulling the handline, or by driving the head block with an electric motor. Various counterweight arbor devices are described in, for example, U.S. Pat. Nos. 3,165,296; 4,134,177; 4,303,237; 5,106,057; 5,531,297; 5,711,713; 6,520,485; 6,537,155; and 6,855,063, the disclosures of which are incorporated herein by reference.
In recent years, manufacturers of counterweight systems have provided counterweight arbors with a sufficient number of spreader plates to allow their interspersing at two-foot intervals in the stack of counterweight plates on the arbor carriage. In the event of an unbalanced or “runaway” arbor, this placement of spreader plates serves to control the forces exerted on the vertical rods of the arbor carriage and prevent the counterweight plates from spilling off the arbor carriage.
Addition of spreader plates to older installed counterweight systems to improve their safety is desirable but would require an expensive and time-consuming dismantling of the arbor apparatus. It would be highly desirable to be able to install additional spreader plates on the arbor apparatus without dismantling it. The present invention provides the benefit of convenient and economical addition of spreader plates to an arbor carriage.